1. Field of the Invention
The present invention relates to an apparatus and method for detecting fluid flow through a solid article. More particularly the present invention is directed to an apparatus and method for determining the presence of fissures or leaks in piping. The present invention is particularly well suited for nondestructive testing of pipe formed from synthetic plastic material.
2. Discussion of the Prior
Synthetic plastic piping has been gradually replacing metallic piping as a conduit for a variety of pressurized and nonpressurized fluids. For example, plastic piping is used for plumbing in general, such as for delivery of drinking water or for sewer lines, or for transmitting fuel. In this regard, certain plastic piping is increasingly being used in the distribution of natural gas. Plastic piping is resistant to galvanic chemical attack which causes corrosion of metallic piping, e.g., corrosive attack by water, soil, mild acids, bases and other electrolytes. The use of plastic piping in the distribution of natural gas provides improved performance primarily as a result of the occurrence of fewer leaks. Additionally, ease of handling, durability and economy are other advantages provided by plastic piping.
Plastic piping sections are molded by variously known techniques such as extrusion or injection molding and are then joined to one another in a variety of ways. For example, plastic pipe used for buried water lines can be manufactured with bell and spigot connections wherein the bell including its gasket cavity is formed during molding as an integral part of the pipe. Other plastic pipe sections can be complementarily molded for threading to one another. Butt fusion of plastic piping sections which involves heating the ends of the sections and forcing the heated ends together whereby a beaded joint is formed upon cooling, has been found efficient and practical for joining most plastic pipe sections. Various types of plastic piping and methods for preparation are described, e.g., by Mruk, S. "Pipe", Encyclopedia of Polymer Science and Engineering, Volume 11, John Wiley & Sons, New York (1988), pages 226-248.
The most prevalent location for occurrence of leaks in a piping system, plastic or otherwise, is at the joints between respective pipe sections. Adequacy of welds and bolted joints in piping systems have been examined by pressurizing the interior of the pipe and measuring any leakage through the weld or joint, i.e., fluid flow from the pressurized pipe, after the pipe has been installed. However, considerable energy consumption has been involved in pressure testing of pipe in this manner. Additionally, it is difficult to remove pipe once it has been installed as part of a fluid distribution system. Accordingly, other methods for leak testing of pipe have been developed. For example, metallic pipe sections can be examined for fissures at the joints by radiography (X-rays) or ultrasound techniques prior to incorporation into a fluid delivery system. However, plastic piping is not sensitive to radiographic analysis, while ultrasound analysis remains difficult and cumbersome to be applied by personnel installing the fluid delivery system. Accordingly, there is a need to develop a technique whereby sections of piping can be easily examined for the presence of potential leaks prior to or during installation as part of a fluid delivery system.